OXIDATION OF IRON FILMS AT 25 K AND THE REACTIVE OXIDATION OF IRON IN SOLID OXYGEN

The oxidation of iron films at approximately 25 K and the reactive formation of iron oxides in a solid oxygen matrix is investigated using synchrotron-radiation-based photoemission. For O2 on Fe, the oxygen molecules dissociate and go into a chemisorbed state. At intermediate oxygen coverages, a disordered divalent FeO-like phase grows at the expense of the chemisorbed state. Further exposures of oxygen lead to the condensation of molecular oxygen on top of the oxide. Initial Fe depositions into a solid molecular oxygen film produce a trivalent Fe2O3-like phase. At higher iron coverages divalent FeO-like and metallic iron phases form because the supply of O2 for the oxide-forming reaction decreases.